Toyota clicking noise

Toyota corola lift back (european) 2001, 75000, 1.4litre. I was wondering if you could help me out. About 2 days ago I noticed a clicking noise coming from the engine when I had the window down. Driving earlier it became alot louder and is very noticeable with all windows up. Its seems to start when I engage 3rd gear but gets louder in 4th and even louder in 5th. There is no clicking in 1st even at 6000rpm and only slightly in 2nd at 6000rpm. There is none in neutral at any rev. Id really appreciate it if you could diagnose it for me as I dont have money for a mechanic and im afraid il do serious damage driving any further.